1. Field of the Invention
This invention relates to a method for conjointly trimerizing cyclopentadiene and methylcyclopentadiene and the utilization of the resultant trimerization product to prepare a high energy fuel.
2. Description of the Prior Art
High energy hydrocarbon fuels are characterized in having a net volumetric heat of combustion in excess of about 140,000 BTU per gallon. A high energy fuel is essentially required for fueling turbojet and ramjet propelled, limited volume missile systems. Beyond the need for a high energy content in order to maximize range performance of the missile, there are other requirements in the forefront depending, in the main, on the manner in which the missile is to be deployed. For instance, in one type of deployment the fuel must exhibit a very low freezing point and low viscosity combined with high volatility characteristics. In another type, relatively low volatility is critical and a higher freezing point and viscosity acceptable.
A high energy hydrocarbon fuel does not occur in nature but rather must be synthesized which generally involves one or more difficult steps. Essentially all of the current generation of such fuels commonly feature a norbornane moiety having an additional cyclic hydrocarbon appendage. The latter includes the norbornane structure itself in the case of the most exotic of these fuels derived from dihydro di (norbornadiene). In some instances only a certain stereo isomer of the synthesized compound represents a suitable fuel from the standpoint of having the requisite physical properties.
Recently, the hydrogenated Diels-Alder trimer of cyclopentadiene and methylcyclopentadiene has been proposed as an acceptable high energy fuel for use in missile systems of the above-mentioned type. A method for preparing such trimers is set forth in U.S. Pat. No. 4,059,644. This prior art method initially involves the partial in situ dissociation of a mixture of the dimers of cyclopentadiene and methylcyclopentadiene to their respective monomers which then in turn randomly adduct with dimers present in reaction mixture to provide a trimerization product. The resultant reaction mixture is hydrogenated directly or alternatively, the trimers are recovered therefrom and hydrogenated to provide the high energy fuel. The shortcoming of this prior art method is that 40-50% of the converted product consists of tetramers and higher oligomers that are unsuitable for use as a missile fuel. It is accordingly the object of this invention to modify the aforesaid prior art method in order to reduce substantially the formation of tetramers and higher oligomers.